Thermoplastic elastomer compositions are hybrid materials of thermoplastic and elastomeric polymers. Thermoplastic elastomer compositions combine desired properties of thermoplastics, for example processability via injection molding or film blowing and/or recyclability, with desired properties of elastomers, for instance high elongation at break, low tensile set and good flex-fatigue resistance.
There are several classes of thermoplastic elastomers. One subset of thermoplastic elastomers are thermoplastic vulcanisates (TPVs), where the elastomeric polymer is dispersed in the thermoplastic phase in the form of discrete vulcanized particles. TPVs are produced by melt-blending thermoplastics with elastomers and curatives in a dynamic vulcanization process. Therefore TPVs are also referred to as dynamically vulcanized alloys (DVAs).
Thermoplastic elastomer compositions from barrier thermoplastics and isobutylene-based elastomers have been considered in industrial applications requiring flexibility and impermeability. EP 0 722 850 B1 discloses a low-permeability thermoplastic elastomeric composition that is excellent as an innerliner in pneumatic tires. This composition comprises a low permeability thermoplastic in which is dispersed a low permeability rubber. EP 0 969 039 A1 discloses a similar composition and teaches that the small particle size rubber dispersed in the thermoplastic was important to achieve acceptable durability of the resulting composition.
Thermoplastic elastomeric compositions particularly useful for tire and other industrial rubber applications have been commercialized by Exxon under the trade name Exxcore DVA Resin. The production of the Exxcore DVA Resin relies on a dynamic vulcanization process for combining a brominated copolymer of isobutylene and methylstyrene (BIMSM) with nylon at a temperature above the nylon melt temperature.
The literature (Bhadane, P. A.; Tsou, A. H.; Cheng, J. and B. D. Favis, Macromolecules 2008, 41, 7549-7559, Tsou, A. H.; Favis, B. D.; Hara, Y.; Bhadane, P. A. and Y. Kirino. Macromol. Chem. Phys. 2009, 210, 340-348; WO2009151859A1) teaches that amine-end groups on the nylon react with the bromomethyl groups on the BIMSM, thereby forming a polyisoprene molecule to which nylon chains have been covalently grafted. Once formed, this graft polymer acts as compatibilizer between the apolar isobutylene containing polymer and the polar barrier thermoplast (nylon). The formation of this graft polymer, which is formed in an in-situ process, is important for the production of a thermoplastic elastomer composition with small particle size rubber dispersed in the thermoplastic. Hence, the grafting reaction between thermoplast and elastomer is important to achieve acceptable durability of the resulting composition in industrial applications. BIMSM, however, is produced in a two-step process comprising (i) the cationic polymerization of isobutylene and methylstyrene to poly(isobutylene-co-methylstyrene) and (ii) bromination of poly(isobutylene-co-methylstyrene) to BIMSM.
EP 0361769 B1 teaches a two-step process for preparing a nylon butyl rubber blend consisting in step (i) preparing a modified butyl rubber by grafting maleic anhydride to chlorinated or non-halogenated butyl rubber and step (ii) the melt-blending of the modified butyl rubber with nylon. The resulting blends offer superior physical properties and superior impermeability compared to a similar blend relying on chlorobutyl rubber and non-halogenated butyl rubber. The processes described in EP 0361769 B1, however, requires at least two different mixing steps in order to achieve the preparation of a nylon butyl rubber blend with desired properties.
WO2009151859A1 describes a process for producing a dynamically vulcanized alloy, the alloy comprising at least one isobutylene-containing elastomer and at least one thermoplastic resin in melt-processing devices (extruders). WO2009151859A1 does not teach grafting reactions between a thermoplastic and non-halogenated polyisobutylene elastomers or butyl rubber elastomers.
US20110054093 describes the use of maleic anhydride modified oligomers, notably polyisobutylene oligomers, in thermoplastic elastomer compositions to match the melt viscosities of the elastomeric and thermoplastic phases. US20110054093 does not teach grafting reactions between a thermoplastic and non-halogenated polyisobutylene elastomers or butyl rubber elastomers.
US 2008076879 (A1) discloses peroxide cured thermoplastic vulcanizates comprising a thermoplastic and an isomonoolefin-multiolefin elastomer, such as butyl rubber. More particularly, the invention relates to peroxide cured thermoplastic vulcanizates wherein the elastomer comprises at least 3.5 mol % of multiolefin in order to facilitate peroxide curing. These thermoplastic vulcanizates are halogen-free.
To improve efficiency and environmental impact it is desirable to provide a process to produce a thermoplastic elastomeric composition using non-halogenated isobutylene-containing elastomers, particularly butyl elastomers, with minimal process steps. Thereby the resources and energy expedited for the modification processes, such as bromination and maleation, applied to the non-halogenated elastomers in order to make them suitable for TPE production would be eliminated. Also, by avoiding the use of halobutyl rubber or regular butyl rubber with sulfur-based curatives in a thermoplastic elastomer composition one also removes the possibility of having the finished article contaminated with extractable organic and/or inorganic halides or sulfides. These enhancements would be of particular benefit for pharmaceutical and consumer goods applications.